Department of Chemical Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan.
ACS Appl Mater Interfaces. 2023 Jul 5;15(26):31692-31702. doi: 10.1021/acsami.3c06128. Epub 2023 Jun 20.
An exciplex, which is composed of electron donor and acceptor molecules and formed by intermolecular charge transfer, is an excited-state species that is able to emit light or transfer its energy to a lower-energy emitter. In reported exciplex-based organic light-emitting diodes (OLEDs), their working mechanism is to generate exciplexes either in the bulk emitting layer (bulk exciplex) or at its interface with an electron transport layer (interface exciplex); both types give promising device performance. Here, we propose a novel strategy of creating both types of exciplexes simultaneously (dual exciplexes) for the generation of more exciplexes for better device performance as indicated in the improved photoluminescence quantum yield (PLQY). Impressively, the dual exciplex-based device with blue thermally activated delayed fluorescence (TADF) emitter 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) exhibits a record-high maximum external quantum efficiency (EQE) of 26.7% among the solution-processed TADF blue OLEDs. By further doping with the red-emitting phosphor emitter into the EML, the white device also gives a record-high EQE of 24.1% among the solution-processed TADF-phosphor hybrid white OLEDs (T-P WOLEDs) with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.34, 0.42), color rendering index of 70, and correlated color temperature of 5198 K. Furthermore, both blue and white devices show an ultralow efficiency roll-off with external quantum efficiencies at a practical brightness value of 1000 cd m (EQE) of 25.1 and 23.9%, respectively. This is the first report of employing a dual exciplex-based OLED with excellent device performance.
激基复合物由电子给体和受体分子组成，通过分子间电荷转移形成，是一种能够发光或将能量转移到低能发射器的激发态物质。在报道的基于激基复合物的有机发光二极管（OLED）中，其工作机制是在体发射层（体激基复合物）或与其电子传输层的界面处（界面激基复合物）生成激基复合物；这两种类型都给出了有前途的器件性能。在这里，我们提出了一种新的策略，可以同时生成这两种类型的激基复合物（双重激基复合物），以生成更多的激基复合物，从而获得更好的器件性能，如改进的光致发光量子产率（PLQY）所示。令人印象深刻的是，基于双重激基复合物的器件具有蓝色热激活延迟荧光（TADF）发射体 9,9-二甲基-9,10-二氢吖啶-2,4,6-三苯基-1,3,5-三嗪（DMAC-TRZ），在溶液处理的 TADF 蓝色 OLED 中，其最大外部量子效率（EQE）达到了 26.7%的记录新高。通过进一步将红色发射磷光体掺杂到 EML 中，白色器件在溶液处理的 TADF-磷光体混合白色 OLED（T-P WOLED）中也给出了记录新高的 EQE 为 24.1%，其国际照明委员会（CIE）坐标为（0.34，0.42），显色指数为 70，相关色温为 5198 K。此外，蓝色和白色器件均显示出超低的效率滚降，在实际亮度值为 1000 cd m 时的外部量子效率（EQE）分别为 25.1%和 23.9%。这是第一个报道采用具有优异器件性能的双重激基复合物基 OLED 的报告。
